Servo steering systems for motor vehicles

In a servo steering system for motor vehicles, comprising, in combination:

• a. a housing provided with a cylinder space and a groove parallel to an axial direction of the cylinder space;
• b. a steering worm shaft operationally connected to a steering wheel, said shaft penetrating the housing and extending into the cylinder space of the housing;
• c. a servo piston axially displacably arranged in the cylinder space for dividing the cylinder space into two separated working spaces, the servo piston being engaged by the worm shaft;
• d. a lever associated with the servo piston, the lever moveable in the axial direction of the servo piston and extending radially away from the axis of the servo piston, the lever having an axial displacement which at least corresponds with the displacement of the servo piston and engaging in the groove provided in housing;
• e. a valve member arranged perpendicularly to the axial direction of the cylinder space and operatively connected to the lever, the lever provided with a recess arranged for permitting minute tilting movements radially relative to the housing when the steering worm shaft is caused to rotate and for, accordingly, operating the valve member and controlling the inflow of pressure to and the outflow of pressure to a return from a working space formed by the servo piston for magnifying in the axial direction of the cylinder space a movement started by the steering worm shaft;
• and
• f. a control piston included in the valve member provided with reaction areas placed under stress for transmitting a feeling of steering to the steering wheel and a driver of the vehicle;
• the improvement wherein:
• g. the servo piston is constructed as a stepped piston having a pair of operational surface of different areas, the working space associated with smaller area operational surface being connected directly to a pressure source, and the larger operational surface associated working space being connected to the pressure source or return line by means of the valve member;
• h. the valve member control piston is provided with a pair of reaction areas, the effective areas of which are substantially in the same ratio as the effective areas of the working spaces of the stepped piston;
• and
• i. said valve member control piston including at least one auxiliary piston which is displacably, spring-centered opposite said groove in the housing for operation by the lever in relation to torque conditions applied by the steering worm shaft.